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At least 793 records · Page 44

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NASA NTRS1972

Artificial laser intensity oscillations associated with beam splitters.

Investigation of the interference-fringe jitter, due to wavelength instability in a laser, that gives rise to pulse-shape blurring intensity variations. The obtained results suggest that the problem can be controlled by using a perfectly flat splitter, or more easily by using a large-angle wedged splitter that either casts many fringes upon the detector element or casts none if the detector is sufficiently far from the splitter.

Kuehn, D. M.↗

NASA NTRS1972

Fracture of boron filaments in an aluminum matrix.

The B-Al composite specimens tested in this study were fabricated by diffusion bonding of 1230 aluminum foil and boron filaments placed in alternate layers, using an acrylic resin solution to maintain filament spacing. The specimens were put under tensile stresses parallel to the filaments, and filament fracture was monitored acoustically under loads. Fracture of specimens under loads was caused by break propagation with a characteristic wedge-type fragmentation pattern indicating its direction. The aluminum foil matrix of the specimens failed by ductile shear type fracture after the break of the filaments.

Steele, J. H.↗

NASA NTRS1972

Correlations of peak heating in shock interference regions at hypersonic speeds.

Correlations are given of measured pressure and heat-transfer peaks for shock/boundary-layer interactions and shear layer attachment on configurations with both two- and three-dimensional interactions. The peak values were obtained from an investigation of shock interference heating on hemispheres, a 30-deg included angle wedge, and a 2.54-cm-diam cylindrical leading-edge fin model. The investigation covers data for Mach numbers of 6 and 20 over freestream Reynolds numbers ranging from (3.3 to 25.6) million per meter, and specific heat ratios of 1.4 and 1.67.

Keyes, J. W.↗

NASA NTRS1972

Transition in compressible free shear layers.

The transition Reynolds number for shear layers produced by interactions between weak and strong shock waves is determined on the basis of experiments performed in a 20-in. (Mach 6) and an 11-in. (Mach 6.9) hypersonic tunnel. A variable angle wedge was used to generate a planar shock wave which interacted with the bow wave of a blunt body. An average value of the transition length (defined as the length along the shear layer from the shock interaction to the point where turbulence became visible on schlieren photographs) was used to determine the transition Reynolds number.

Birch, S. F.↗

NASA NTRS1972

Stresses in bonded materials with a crack perpendicular to the interface.

The problem of two elastic bonded half planes containing a crack perpendicular to the interface is considered. First the solution for the semi-infinite crack under concentrated wedge loading is given. Then the problem of a finite crack fully imbedded in one of the half planes of terminating at the interface is considered. The Mellin transform in conjunction with the dislocations is used to formulate the problem and to derive the integral equation. The integral equation is solved; the stress intensity factors, the crack surface displacement, and the stresses around the crack tip terminating at the interface are obtained. Noting that the power of the singularity for the interface tip of the crack is not -1/2, a tentative fracture criterion dealing with the initiation of fracture propagation is proposed.

Cook, T. S.↗

NASA NTRS1973

High-friction mechanical grips

Plasma-arc spraying offers method of preparing required surface at greatly reduced cost. Coarse-grained, tungsten carbide bonded-nickel coating is applied by spraying. Coating has been used successfully on wedge-shaped mechanical test grips.

Stevens, E. G.↗

NASA NTRS1972

Measured and calculated mean flow properties of a two-dimensional, hypersonic, turbulent wake

The hypersonic turbulent wake produced by a wedge was studied experimentally and its properties were compared with predictions obtained from a numerical computation procedure. In the computation procedure several models for the eddy viscosity formulation of the turbulent transport were examined. Conventional-defect models and a modified mixing-length model were found to yield good predictions of the experimental data. The classical mixing-length model gave unrealistic results. The experimental data displayed similarity when velocity and temperature defects were scaled by the maximum defects and the transverse coordinate was scaled by the velocity-defect half-width.

Wagner, R. D.↗

NASA NTRS1973

Static penetration resistance of soils

Model test results were used to define the failure mechanism associated with the static penetration resistance of cohesionless and low-cohesion soils. Knowledge of this mechanism has permitted the development of a new analytical method for calculating the ultimate penetration resistance which explicitly accounts for penetrometer base apex angle and roughness, soil friction angle, and the ratio of penetration depth to base width. Curves relating the bearing capacity factors to the soil friction angle are presented for failure in general shear. Strength parameters and penetrometer interaction properties of a fine sand were determined and used as the basis for prediction of the penetration resistance encountered by wedge, cone, and flat-ended penetrometers of different surface roughness using the proposed analytical method. Because of the close agreement between predicted values and values measured in laboratory tests, it appears possible to deduce in-situ soil strength parameters and their variation with depth from the results of static penetration tests.

Durgunoglu, H. T.↗

NASA NTRS1973

Analysis of a two-dimensional type 6 shock-interference pattern using a perfect-gas code and a real-gas code

Numerical codes were developed to calculate the two dimensional flow field which results when supersonic flow encounters double wedge configurations whose angles are such that a type 4 pattern occurs. The flow field model included the shock interaction phenomena for a delta wing orbiter. Two numerical codes were developed, one which used the perfect gas relations and a second which incorporated a Mollier table to define equilibrium air properties. The two codes were used to generate theoretical surface pressure and heat transfer distributions for velocities from 3,821 feet per second to an entry condition of 25,000 feet per second.

Bertin, J. J.↗

NASA NTRS1973

Corner pressures and fillet shock locations for symmetrical corners by an approximate method.

Description of an approximate method for predicting the pressure in the immediate corner region and the shock structure on stream-aligned, sharp-leading-edge, symmetrical corner configurations. The method is basically the two-shock method developed by Charwat and Redekopp (1966), with the additional assumption that the corner fillet shock can be located from the calculated pressure in the corner. Corner pressures are correlated over a wide range of Mach numbers in air and helium for different corner wedge angles. The shock structure calculated by this method is compared with supersonic and hypersonic data.

Watson, R. D.↗

NASA NTRS1973

Base pressure in laminar supersonic flow.

An asymptotic description is proposed for supersonic laminar flow over a wedge or a backward-facing step, for large Reynolds number and for a base or step height which is small compared with the boundary-layer length. The analysis is carried out for adiabatic wall conditions and a viscosity coefficient proportional to temperature. In a particular limit corresponding to a very thick boundary layer, a similarity law is obtained for the base pressure. For a thinner boundary layer an asymptotic form for the base pressure is obtained which shows the dependence on the parameters explicitly and which permits good agreement with experiment. This latter result is based on an inviscid-flow approximation for the corner expansion and for reattachment with viscous forces important primarily in a thin sublayer about the dividing streamline. A prediction of the pressure distribution at reattachment is given and the result is compared with experimental pressure distributions.

Messiter, A. F.↗

NASA NTRS1974

Experimental study of sharp and blunt nose streamwise corners at Mach 20

Extensive heat transfer and pressure distribution data and oil flow studies on sharp and blunt-nose streamwise corners at Mach 20 in helium are presented. The far corner boundary layers on the wedge surfaces forming the corners are laminar for most test conditions. Analysis of the data indicates that the corner flow field geometry can be described in terms of the inviscid shock pattern on the two dimensional surfaces forming the corner. Parameters used to correlate blunt shock growth can be used to correlate features of the flow field observed in oil flow photographs in addition to the measured pressure and heat transfer distributions on the models. The flow field structure is described from available experimental data. Regions of the flow in which the structure still is not known are discussed.

Watson, R. D.↗

NASA NTRS1974

Calculation of supersonic stream parameters of a real gas from measurable quantities using FORTRAN 4 routines

Sets of routines are presented that calculate such real-gas supersonic stream properties as velocity, density, enthalpy, entropy, and isentropic exponent. Two alternative sets of measurements are assumed: (1) stagnation pressure, stagnation temperature, and the pressure on the surface of a static-pressure wedge; or (2) pressure and temperature in a plenum upstream of a supersonic nozzle and the stagnation pressure at the exit of this nozzle. The routines are applicable to any gas whose properties are known. Explicit routines are presented for determining these properties for air, nitrogen, oxygen, normal hydrogen, para-hydrogen, helium, argon, steam, methane, and natural gas.

Johnson, R. C.↗

NASA NTRS1974

The radiation from slots in truncated dielectric-covered surfaces

A theoretical approach based on the geometrical theory of diffraction is used to study the electromagnetic radiation from a narrow slot in a dielectric-covered perfectly-conducting surface terminated at an edge. The total far-zone field is composed of a geometrical optics field and a diffracted field. The geometrical optics field is the direct radiation from the slot to the field point. The slot also generates surface waves which are incident at the termination of the dielectric cover, where singly-diffracted rays and reflected surface waves are excited. The diffraction and reflection coefficients are obtained from the canonical problem of the diffraction of a surface wave by a right-angle wedge where the dielectric-covered surface is approximated by an impedance surface. This approximation is satisfactory for a very thin cover; however, the radiation from its vertical and faces cannot be neglected in treating the thicker dielectric cover. This is taken into account by using a Kirchhoff-type approximation, which contributes a second term to the diffraction coefficient previously obtained. The contributions from the geometrical optics field, the singly-diffracted rays and all significant multiply-diffracted rays are summed to give the total radiation. Calculated and measured patterns are found to be in good agreement.

Hwang, Y. M.↗

NASA NTRS1974

An interdisciplinary study of the estaurine and coastal oceanography of Block Island Sound and adjacent New York coastal waters

ERTS-1 photographic data products have been analyzed using additive color viewing and electronic image analysis techniques. Satellite data were compared to water sample data collected simultaneously with the data of ERTS-1 coverage in New York Bight. Prediction of the absolute value of total suspended particles can be made using composites of positives of MSS bands 5 and 6 which have been precisely made using the step wedge supplied on the imagery. Predictions of the relative value of the extinction coefficient can be made using bands 4 and 5. Thematic charts of total suspended particles (particles per litre) and extinction coefficient provide scientists conducting state and federal water sampling programs in New York Bight with data which improves the performance of these programs.

Yost, E.↗

NASA NTRS1974

Interference heating from interactions of shock waves with turbulent boundary layers at Mach 6

An experimental investigation of interference heating resulting from interactions of shock waves and turbulent boundary layers was conducted. Pressure and heat-transfer distributions were measured on a flat plate in the free stream and on the wall of the test section of the Langley Mach 6 high Reynolds number tunnel for Reynolds numbers ranging from 2 million to 400 million. Various incident shock strengths were obtained by varying a wedge-shock generator angle (from 10 deg to 15 deg) and by placing a spherical-shock generator at different vertical positions above the instrumented flat plate and tunnel wall. The largest heating-rate amplification factors obtained for completely turbulent boundary layers were 22.1 for the flat plate and 11.6 for the tunnel wall experiments. Maximum heating correlated with peak pressures using a power law with a 0.85 exponent. Measured pressure distributions were compared with those calculated using turbulent free-interaction pressure rise theories, and separation lengths were compared with values calculated by using different methods.

Johnson, C. B.↗

NASA NTRS1974

Apollo data analysis experiment S-211. Low brightness image data analysis

The scientific analyses of photographic data in astronomy obtained by the Apollo Orbital Science Photographic Team during Apollo flights 14 through 17 are described. Some of the tasks are the collection and correlation of Quick-Look listings, working prints for further study, the generation of post-mission reports, and project reports. Postflight calibrations of the flight photographic systems are carried out, and lens vignetting effects are corrected. The data handling is described and includes photodigitization of photographic scenes, calibrated step-wedges, and vignetting patterns, which are followed by computer program processing of the film density readings.

Mercer, R. D.↗

NASA NTRS1973

A note on the unsteady cavity flow in a tunnel

The unsteady internal cavitating flow such as the one observed in a pump or a turbine is studied for a simple two-dimensional model of a base-cavitating wedge in an infinite tunnel and it is shown how the cavitation compliance can be calculated using the linearized free streamline theory. Numerical values are obtained for the limiting case of a free jet. Two important features are: First, the cavitation compliance is found to be of complex form, having additional resistive and reactive terms beyond the purely inertial oscillation of the whole channel in 'slug flow.' Second, the compliance has a strong dependence on frequency.

Kim, J. H.↗